Birthday party girls only

I'm planning my daughter 3rd bday. We are thinking in having a ballet party. With her ballet teacher coming to show some moves.

I would like just to invite my daughter's girlfriends, but I really don't know if this is right. I'm in a mommy group (10 kids. Half are boy are half girls) so wondering if will be rude to leave the boys out and just considering the girls.

Also, when they have boy sibilings can you invite just the sisters?